Orthopaedic surgical instrument

ABSTRACT

An orthopaedic surgical instrument comprising an internal support about which a plastic substrate is disposed, and which includes exposed cutting surfaces relative to the plastic substrate. The surgical instrument may have a generally hemispherical shape and the internal support may comprise a non-planar shim. In particular embodiments the shim includes multiple interconnected limbs with multiple holes or slots disposed in the limbs and with the holes or slots including the cutting surfaces.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.11/997,358, which is a national stage application under 35 U.S.C. 371 ofPCT Application No. PCT/GB2006/003029 having an international filingdate of Aug. 14, 2006, which designates the United States, which PCTapplication claimed the benefit of United Kingdom Application Serial No.0516625.1, filed Aug. 15, 2005, the entire disclosure of each of whichis hereby incorporated herein by reference

This invention relates to the field of instruments used in orthopaedicsurgery for example, but not limited to, acetabular reamers, femoralreamers, broaches/rasps etc. The present invention may be equallyapplicable to other instruments used in hip, knee, spinal, shoulder,elbow, trauma and toe surgery, for example.

BACKGROUND

Acetabular reamers are surgical tools which are used to cuthemispherical cavities in pelvis bones for the insertion of artificialhip joints. The reamer comprises a hemispherical reamer cup, made fromsurgical stainless steel, having a complex arrangement of cuttingsurfaces extending outwardly from the hemispherical cup. The reamer cupis attachable to a drive shaft or handle, which in turn can be attachedto a drill or the like to provide rotational force.

Acetabular reamers must be capable of producing cavities of very precisedimensions and consequently, the cutting surfaces are generally drilled,worked and sharpened by hand in order to give the required precision.Therefore the manufacturing process for conventional acetabular reamercups is very skilled, labour-intensive and hence so expensive that it isnot economical for the reamer to be disposable. This means that thereamer cup must be intensively cleaned after each use. The cuttingsurfaces may periodically require re-sharpening as a result of wear inuse and/or during cleaning, the re-sharpening being a labour-intensiveand skilled task in itself. An example of such a conventional reamer isdescribed in U.S. Pat. No. 4,811,632.

Not only must the reamer cup be cleaned after each use, but also thereusable handle or drive shaft. The junction between the reamer cup andthe drive shaft or handle is particularly difficult to clean as it maytrap bone particles, dried blood and/or other debris. The interior ofthe reamer cup described in U.S. Pat. No. 4,811,632 has a cylindricalsurface which engages coaxially with the drive shaft, the two beingremovably secured together by means of a pair of pins extending throughholes therein. Alternatively, the reamer cup could be mounted to thedrive shaft by engaging threads or discrete fasteners or otherequivalent means. All of these moving parts and components providelocations where debris could become trapped, presenting contaminationrisk and/or problems in fitting the parts together. Undesirable freeplay between the cup and drive shaft increases wear and decreases theprecision of the reamer.

Therefore, it is desirable to provide a simplified and preferablydisposable reamer such as that described in U.S. Pat. No. 5,100,267. InU.S. Pat. No. 5,100,267, a disposable reamer cup is provided for usewith a reusable drive shaft or handle, wherein the reamer cup isprovided with a polymeric plug into which the drive shaft is fitted. Thepolymeric plug is joined to the reamer cup by detents and intrusionsthereon. The drive shaft is attached to the polymeric plug in the samemanner as described in U.S. Pat. No. 4,811,632 and, although containingless metal because of the use of the polymeric plug, the reamer cup ismanufactured in the same way as described in U.S. Pat. No. 4,811,632.

Consequently, the metal reamer cup is still made using alabour-intensive method, necessary in order to provide the accuratelyplaced cutting surfaces. Furthermore, the number of moving parts andcomponents in the junction between the reamer cup and the drive shaft isnot addressed.

It is therefore desirable to provide an improved disposable acetabularreamer or other surgical instrument which seeks to alleviate thedisadvantages of the above-described prior art.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided amethod of manufacturing an orthopaedic surgical instrument comprisingthe steps of

-   -   forming a generally planar shim having a predetermined shape;    -   creating a plurality of holes or slots in the plane of the shim;    -   temporarily shielding said holes or slots from a plastic        moulding process;    -   overmoulding said shim with a plastic substrate using said        plastic moulding process; creating a cutting surface at each of        said holes or slots.

Preferably the step of creating the cutting surfaces occurs before saidshielding and overmoulding steps. Alternatively, the cutting surfacescan be created after overmoulding, as a final step in the manufacture ofthe orthopaedic surgical instrument.

Preferably, said plastic moulding process is injection moulding and/orsaid plastic is free-flowing acetal.

In a preferred embodiment, said plastic substrate is moulded to at leastpart of the exterior surface of said shim. Alternatively, said shim isencapsulated by said plastic substrate i.e. having plastic moulded toboth the exterior and interior surfaces of said shim. A furtheralternative embodiment, in which the substrate is moulded to aperipheral flange is described below.

Preferably, said holes or slots are created by pressing or punchingthrough said shim. The cutting surfaces may also be created by pressingor punching through said shim, or alternatively the cutting surfaces maybe formed using a broach. The shim is preferably metal, preferablysurgical stainless steel or titanium but may also be made from suitableplastics e.g. PEEK.

In a preferred embodiment, said holes or slots and/or cutting surfacesare temporarily shielded from said plastic moulding process using amould tool of complementary shape to said shim and said holes or slotsand/or cutting surfaces.

Preferably, the method further comprises the step of bending said shiminto a non-planar shape before overmoulding the plastic substrate.Separately, or in a simultaneous bending step, the method may furthercomprise the step of bending said shim to form a peripheral flangethereon with a raised section therebetween.

In one embodiment, the orthopaedic surgical instrument is an acetabularreamer cup and wherein said non-planar shape is a generallyhemispherical shape.

In a preferred embodiment, the plastic substrate is moulded to theexterior surface of the peripheral flange, preferably so that the uppersurface of the substrate is substantially flush with the raised sectionof the shim. In this way, the cutting surfaces (or the holes/slots wherethe cutting surfaces will be formed) are fully exposed and free ofplastic.

Preferably, said generally planar shim is a cross-shape. However, thisis non-limiting any suitable shape for the shim can be selectedaccording to the circumstances, as can the number and location of theholes or slots and/or cutting surfaces provided thereon.

According to a second aspect of the invention, there is provided asurgical instrument manufactured using the method of any of thepreceding paragraphs. Preferably, the surgical instrument is anacetabular reamer cup.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will now be moreparticularly described, by way of example only, with reference to theaccompanying drawings in which:

FIG. 1 is a perspective view of a metal shim for use in the method ofthe present invention;

FIG. 2 is a perspective view of the metal shim of FIG. 1, in which holeshave been formed;

FIG. 3 is a perspective view of the metal shim of FIG. 1, in whichcutting surfaces have been formed;

FIG. 4 is a perspective view of the metal shim of FIG. 3, having beenpressed into a generally hemispherical shape;

FIG. 5 is a perspective view of the metal shim of FIG. 4 illustratinghow a mould tool shields one cutting surface during the mouldingprocess;

FIG. 6 is a cross-sectional side view of the mould tool and cuttingsurface of FIG. 5;

FIG. 7 is a cross-sectional view through the mould tool and cuttingsurface of FIG. 5;

FIG. 8 is a perspective view, from below of part of the mould tool usedto shield a cutting surface during the moulding process (the cuttingsurface is not illustrated);

FIG. 9 is a perspective view of a the metal shim of FIG. 4 to which aplastics substrate has been overmoulded, resulting in a composite reamercup;

FIG. 10 is a top view of the reamer cup of FIG. 9;

FIG. 11 is a perspective view of the metal shim of FIG. 2, having beenpressed into a generally hemispherical shape;

FIG. 12 is a top view of the shim of FIG. 11;

FIG. 13 is a perspective view of part of a mould tool;

FIG. 14 is a perspective view of a the metal shim of FIGS. 11 and 12 towhich a plastics substrate has been overmoulded and on which cuttingsurfaces have been formed, resulting in a composite reamer cup;

FIG. 15 is an exploded view of the reamer cup, connector and driveshaft, showing how they fit together, in use.

DETAILED DESCRIPTION

Throughout the description and claims of this specification, the words“comprise” and “contain” and variations of the words, for example“comprising” and “comprises”, means “including but not limited to”, andis not intended to (and does not) exclude other components, integers orsteps.

Throughout the description and claims of this specification, thesingular encompasses the plural unless the context otherwise requires.In particular, where the indefinite article is used, the specificationis to be understood as contemplating plurality as well as singularity,unless the context requires otherwise.

Features, integers, characteristics, or groups thereof described inconjunction with a particular aspect, embodiment or example of theinvention are to be understood to be applicable to any other aspect,embodiment or example described herein unless incompatible therewith.

Throughout this description, the term “shim” is used to describe anyrelatively thin, generally flat or planar item, preferably made frommetal, which is used as a template or blank to form the basis of theinstrument manufactured according to the method described herein. Thisdescription is provided solely to aid the reader and should not beconstrued to have a scope less than that understood by a person skilledin the art or as limiting the scope of the appended claims.

Referring to FIG. 1, a generally planar shim 1 is pressed from a sheetof metal. The shim could be any desired shape but, in the illustratedembodiment, is generally cross-shaped. A cross-shaped shim need not haveequal angles between all four of its limbs. Suitable metals includesurgical stainless steel or titanium, for example, and the metal sheetfrom which the shim 1 is pressed is typically of 0.2-0.5 mm thickness.Alternatively, instead of metal, the shim could be formed from asuitable plastic such as PEEK (polyetheretherketone).

The second stage of the manufacturing method is illustrated in FIG. 2.Holes 2 are punched, pressed or otherwise cut through the shim 1 inspecifically determined positions. Any desired pattern can be used,depending upon the shape of the shim 1 and the intended finalapplication for the surgical instrument; however, the holes 2 determinethe locations of the cutting surfaces of the finished surgicalinstrument and therefore need to be located with accuracy. The holes 2may be in the form of generally C-shaped or D-shaped slots, asillustrated, but other configurations are suitable as will beappreciated by a person skilled in the art. C-shaped slots mean thatthere is a tongue 2A which can be readily bent out of the plane of theshim to form a cuffing surface, when desired.

Two alternative embodiments of the remaining steps of the manufacturingmethod will now be described.

The first alternative embodiment is described with reference to FIGS.3-10. Referring to FIG. 3, the next stage of the method is to form thecutting surfaces. At the location of each hole 2, metal remaining afterthe hole has been formed is bent out of the plane of the shim 1 in orderto form a cutting surface 3. The shape and orientation of each cuttingsurface 3 is selected according to the shape of the shim 1 and theintended final application for the surgical instrument. Since the metalshim 1 is relatively thin (compared with the 1-1.5 mm thickness of aprior-art acetabular reamer cup), the cutting surfaces 3 may well besharp enough for their intended purpose already, once formed, andtherefore will not require additional sharpening by hand. However, ifdesired, a sharpening stage may be included in the manufacturing method,wherein the cutting surfaces 3 are sharpened by an automated process.

Once the cutting surfaces 3 have been formed (and sharpened ifnecessary), the shim 1 is put into a press in order to bend it into agenerally hemispherical shape, as illustrated in FIG. 4.

Having bent the shim 1 to the desired shape, the shim is placed in aninjection moulder. A specially-designed mould tool is needed in order totemporarily shield the holes 2 and cutting surfaces 3 from the injectionmoulding process to prevent them filling with plastics, as both theholes and cutting surfaces obviously need to be exposed and free ofplastics in the finished acetabular reamer.

Referring to FIGS. 5-8, part of a mould tool 40 is illustrated to showhow the exterior of a cutting surface 3 is shielded from the mouldingprocess. The mould tool 40 has a cavity 41 therein, in which the cuttingsurface 3 is located. The cavity 41 is defined by walls 42 which abutclosely with the exterior surface of the shim 1. An undercut 43 definesthe area into which plastics will flow during the moulding process, theclose abutment between walls 42 and the exterior surface of the shim 1preventing plastics from flowing into cavity 41.

For illustrative purposes, the shielding of only one cutting surface isshown in FIGS. 5-8, however in practice every cutting surface issimilarly shielded and the whole moulding tool 40 has a generallyhemispherical outer shape.

The interior of each cutting surface 3 also needs to be shielded fromthe moulding process. In one embodiment, this is achieved by using aspherical or hemispherical mould tool (not illustrated) which is closelylocated against the interior of shim 1 so as to prevent plastics fromcontacting any part of the interior of the shim during the mouldingprocess. In an alternative embodiment, a mould tool (not illustrated) isused which is complementary in shape to that illustrated in FIG. 5 i.e.generally hemispherical and having cavities (equivalent to cavities 41)and walls (equivalent to walls 42) on the outer surface thereof whichsurround the holes 2 so as to prevent ingress of plastics. In thisalternative embodiment, a reamer cup is formed in which the shim 1 isentirely encapsulated by the plastics substrate.

After the injection moulding process is completed, the mould tool 40 isremoved, leaving a composite surgical instrument having an internalmetal support [the shim 1], exposed metal cutting surfaces 3 and aplastics substrate 4.

As shown in FIGS. 9 and 10, after injection moulding, the shim 1 iscovered (first embodiment) or encapsulated (alternative embodiment) by aplastics substrate 4 approximately 2.5 mm thick. In all embodiments, thecutting surfaces 3 are exposed. In this way, there is provided anacetabular reamer cup which is much more lightweight than the prior artreamer cups which are entirely made from metal. Metal shim 1 is thinnerthan the metal prior art reamer cups as it only needs to be ofsufficient thickness to support the plastics substrate.

The second embodiment is described with reference to FIGS. 11-14. Takingthe shim illustrated in FIG. 2, the shim is bent in a moulding tool orpress (not illustrated) in order to bend it into a generallyhemispherical shape as illustrated in FIG. 11. Simultaneously, or in aseparate bending operation, a profile is bent transversely onto eachlimb of the shim, so that each limb has peripheral flanges 5 and araised section 6 therebetween.

Having bent the shim 1 to the desired shape, the shim is placed in aninjection moulder. A specially-designed mould tool is needed in order totemporarily shield the holes 2 from the injection moulding process toprevent them filling with plastics, as the holes need to be exposed andfree of plastics after overmoulding, so that exposed cutting surfacescan be formed in the finished acetabular reamer.

Part of a suitable mould tool is illustrated in FIG. 13. The mould tool50 has the same generally hemispherical shape as the bent shim 1. Themould tool is provided with a plurality of raised pads 51 over itssurface. Importantly, these pads 51 are located such that they willalign with the holes 2 of the bent shim 1, when the bent shim is placedon top of the mould tool 50. Preferably, the raised pads 51 fit closelyinside the raised section 6 of the bent shim. In this way, the pads 51effectively shield the underside of the raised section 6 in the vicinityof each hole 2 so that plastic does not encroach there during injectionmoulding. The underside of the raised section between the holes 2 (i.e.between the pads 51) is not shielded and therefore plastic can encroachthere during injection moulding.

The top surface of the raised section 6 is shielded from the injectionmoulding plastics by means of a mating mould tool which iscorrespondingly hemispherical and which mates with the illustrated mouldtool 50. When in position, the mating mould tool is in contact with thewhole of the top surface of the raised section 6 so that it is shieldedfrom the moulding process. The peripheral flanges 5 are not shielded bythe mating mould tool and therefore plastic can encroach there duringinjection moulding.

FIG. 14 shows how, after injection moulding, the shim 1 is covered by aplastics substrate 4 approximately 2.5 mm thick. The raised section 6 ofthe shim is exposed and preferably flush with the top surface of thesubstrate.

Cutting surfaces 3 are formed at each of the holes 2, for example usinga broach.

In either embodiment, the plastic used in the injection moulding stageis preferably free-flowing acetal, although any medical-grade approvedplastic may potentially be used.

FIG. 15 shows how the finished reamer cup 10 is attached to a driveshaft 30. The cutting surfaces 3 are not illustrated in the schematicFIG. 15. The reamer cup 10 is attached to the drive shaft 30 by means ofa generally annular connector 20.

The rim of the hemispherical reamer cup is provided with twodiametrically located notches 11. The annular connector 20 is providedwith two diametrically located resiliently flexible arms 21 which can beradially flexed inwardly by applying radially-inward finger pressure topads 23, which are attached to the arms 21. Each of the flexible arms 21is provided with a radially-protruding tag 22 at the extremity thereof.

In order to fit the connector 20 to the reamer cup 10, pads 23 aresqueezed together so that flexible arms 21 (and hence tags 22) are movedradially-inwardly. The connector 20 is placed inside the rim of thereamer cup 10 with the tags 22 aligned with the notches 11. The pads 23are then released so that the resiliently flexible arms 21 moveradially-outwardly so that tags 22 locate in notches 11, thus holdingthe reamer cup 10 and connector 20 together.

One end of the drive shaft 30 is provided with two diametrically locatedresiliently flexible arms 31 which can be radially flexed inwardly byapplying radially-inward finger pressure to pads 33, which are attachedto the arms 31. Each of the flexible arms 31 is provided with aradially-protruding tag 32 at the extremity thereof.

In order to fit the drive shaft 30 to the connector 20, pads 33 aresqueezed together so that flexible arms 31 (and hence tags 32) are movedradially-inwardly. The end of the drive shaft 30 is placed inside theannular connector 20 with the tags 32 aligned with notches 24 which arediametrically located on the interior surface of the connector 20. Thepads 33 are then released so that the resiliently flexible arms 31 moveradially-outwardly so that tags 32 locate in notches 24, thus holdingthe connector 20 and drive shaft 30 together. The tags 32 are preferablyV-shaped (as illustrated) or similar so as to prevent relative axialmovement of the connector 20 and drive shaft 30.

In this way, the reamer cup, connector and drive shaft are releasablyattached to one another in such a way that a rotational driving forcecan be transmitted from the drive shaft 30 to the reamer cup 10. Thereis no need for pins, clips or other moving parts in order to fix thecomponents together, the only moving parts being the flexible arms 21and 31. The significant decrease in the number of components and movingparts greatly facilitates the cleaning of the connector and drive shaft(both of which can be reusable).

In use, the reamed bone particles might need to be retained and theparticles can be readily retained within the hemispherical reamer cup.

The above-described method provides a greatly simplified and morecost-effective method of manufacturing surgical instruments, inparticular a disposable acetabular reamer cup. The surgical instrumentthus produced contains much less metal than conventionally-manufacturedinstruments and does not require hand-working, The cost-effective natureof the manufacturing method means that the instruments can bedisposable. The method may equally be suitable for the manufacture ofother orthopaedic surgical instruments, for example broaches/rasps,femoral reamers etc.

What is claimed is:
 1. An orthopaedic surgical instrument, saidinstrument comprising: a non-planar shim having a plurality of holes orslots; a plastic substrate molded about said shim with a plurality ofsaid holes or slots being exposed; wherein said exposed holes or slotsin said shim include cutting surfaces.
 2. The surgical instrument ofclaim 1, wherein said non-planar shim has a generally hemisphericalshape.
 3. The surgical instrument of claim 1, wherein said shim includesa plurality of connected limbs.
 4. The surgical instrument of claim 3,wherein said shim is generally cross-shaped.
 5. The surgical instrumentof claim 1, wherein said exposed holes or slots comprise closed holes orslots that are bounded by said shim about the perimeters of said exposedholes or slots.
 6. The surgical instrument of claim 1, wherein saidcutting surfaces are formed at said hole or slot on a portion of saidshim that is bent relative to the adjacent surface of said shim.
 7. Thesurgical instrument of claim 1, wherein said shim includes a peripheralflange with a raised section there between.
 8. The surgical instrumentof claim 7, wherein said plastic substrate is molded to the exteriorsurface of said peripheral flange.
 9. An orthopaedic surgicalinstrument, said instrument comprising; a shim having a plurality ofconnected limbs and a generally hemispherical shape, said shim having aplurality of holes or slots disposed on said limbs; a plastic substratemolded about said shim with a plurality of said holes or slots beingexposed; wherein said exposed holes or slots in said shim includecutting surfaces.
 10. The surgical instrument of claim 9, wherein saidshim is generally cross-shaped.
 11. The surgical instrument of claim 9,wherein said exposed holes or slots comprise closed holes or slots thatare bounded by said shim about the perimeters of said exposed holes orslots.
 12. The surgical instrument of claim 9, wherein said cuttingsurfaces are formed at said hole or slot on a portion of said shim thatis bent relative to the adjacent surface of said shim.
 13. The surgicalinstrument of claim 12, wherein said plastic substrate forms a generallyhemispherical shape about said shim, and wherein said cutting surfacesextend above the hemispherical surface of said plastic substrate. 14.The surgical instrument of claim 9, wherein said shim includes aperipheral flange with a raised section there between.
 15. The surgicalinstrument of claim 14, wherein said plastic substrate is molded to theexterior surface of said peripheral flange.
 16. The surgical instrumentof claim 9 further including a rim, and wherein said rim includesnotches, said notches adapted for connecting said surgical instrumentwith a drive shaft.
 17. An orthopaedic surgical instrument, saidinstrument comprising: a plastic substrate formed about a metal support,said plastic substrate having a generally hemispherical shape; andcutting surfaces formed in said metal support and exposed relative tosaid plastic substrate.
 18. The surgical instrument of claim 17, whereinsaid metal support includes a plurality of holes or slots with saidcutting surfaces formed at said holes or slots on a portion of said shimthat is bent relative to the adjacent surface of said shim.
 19. Thesurgical instrument of claim 18, wherein said cutting surfaces extendabove the hemispherical surface of said plastic substrate.
 20. Thesurgical instrument of claim 17, wherein said metal support includes aplurality of connected limbs and a plurality of holes or slots disposedon said limbs with said cutting surfaces being formed at said holes orslots.